For that, most likely what's happening is it's delivering hangup messages. Although 300 missed calls in a period of 2 days is a bit hard to believe, but I'll assume you're exaggerating.
Voice Processor > Devices > Mailboxes > (Mailbox #) > Deliver Hangup Messages (When ANI is available) - No
Do this for each mailbox that's getting these excess "phantom" messages.
I have dreamed a dream, but now that dream has gone from me.